Field of the Invention
The present invention relates to an image processing apparatus and control method therefor.
Description of the Related Art
There is an increasing frequency of printing of data generated by a personal computer and the like using an image processing apparatus with a printing function. At the time of printing, the image processing apparatus forms an image using a recording agent, such as toner and ink, in accordance with an inkjet recording method, an electrophotographic method, or other image forming methods. The amount of consumption of the recording agent, such as toner and ink, greatly influences a running cost; in view of this, there are known image processing apparatuses that have a recording agent saving mode called an ink saving mode, a toner saving mode, and the like for the purpose of reducing the amount of consumption of the recording agent.
There are common methods for achieving such a reduction in the amount of consumption of the recording agent, one example being a method for reducing the amount of consumption of the recording agent by executing dot thinning processing through application of hatching processing to the entirety of image data when a recording agent saving mode has been selected. There is also a method for reducing the amount of consumption of the recording agent by executing density conversion processing at the time of printing in such a manner that, when a recording agent saving mode is selected, density conversion processing that is different from the one used in a normal printing mode is executed so as to lower the output density.
However, in the recording agent saving modes according to the foregoing conventional methods, the amount of consumption of the recording agent is reduced for the entirety of image data, and therefore the density of a whole image becomes lower than that of an image printed in a normal printing mode, which results in a decreased printing quality. Especially, in a character portion of image data, the decreased printing quality could possibly make it difficult to read characters. Accordingly, there is a need for a method for further suppressing a decrease in the printing quality, especially in a character portion of image data, while reducing the amount of consumption of the recording agent.
In view of this, an image forming apparatus of Japanese Patent Laid-Open No. 2005-234391 (hereinafter Document 1) executes region determination processing for determining whether a region is a character region or a photograph region based on feature data included in image data, and in a recording agent saving mode, decides on a deletion rate at which pixels to be recorded are deleted for each of the character region and the photograph region. At this time, an edge portion of a character image is enhanced by making the deletion rate for an edge portion lower than the deletion rate for a non-edge portion of the character region. On the other hand, a uniform deletion rate is set for an edge portion and a non-edge portion of the photograph region, because enhancing the edge portion of the photograph region triggers deterioration in the image quality, such as tone reversal. In this way, Document 1 achieves a recording agent saving mode that suppresses a decrease in the printing quality of a character image while suppressing edge enhancement processing from unfavorably influencing a photographic image.
In Document 1 described above, by making a determination of a character region or a photograph region and switching to recording agent reduction processing (a deletion rate of pixels to be recorded) corresponding to the character region or the photograph region, a decrease in the legibility of characters is suppressed when a recording agent saving mode has been set. As described above, the image processing apparatus disclosed in Document 1 makes a determination of the character region or the photograph region based on the result of analysis on an image feature amount. However, in reality, it is difficult to determine regions of a character image and a photographic image with high precision in an image where the character image and the photographic image coexist. Especially, determining an image region at low cost leads to a high possibility of an erroneous determination of the image region, and such an erroneous determination triggers deterioration in the image quality, such as a decrease in the legibility of a character image, and tone reversal in a photographic image.